Atheism

If you fat shame a person, it could bring motivation to become healthier.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6565398/

"exposure to weight bias triggers physiological and behavioural changes linked to poor metabolic health and increased weight gain."

"The more people are exposed to weight bias and discrimination, the more likely they are to gain weight and become obese, even if they were thin to begin with"

"Fat shaming is also linked to depression, anxiety, low self-esteem, eating disorders and exercise avoidance"

What you are advocating for directly leads to higher rates of obesity.

Being fat is objectively bad for your health. Sure. But being sexually active is objectively good for your health.

Shaming anyone though, rarely leads to any positive change. Probably the opposite.